The role of L1cam in murine corticogenesis, and the pathogenesis of hydrocephalus

L1cam (L1), one of the cell adhesion molecules belonging to the immunoglobulin superfamily, plays critical roles in neuronal migration, axon growth, guidance, fasciculation, and synaptic plasticity in the central as well as the peripheral nervous system. A number of X‐linked forms of mental retardation have been associated with mutations in the L1 gene, including X‐linked hydrocephalus in humans. Although model mice with different sites of L1 mutation have been studied, the pathogenetic mechanisms of hydrocephalus and mental retardation still remain unsolved. We herein present an overview of the function of L1 in the central nervous system and describe a human case of L1 mutation and knock‐in mice that showed deleted sixth immunoglobulin of L1. Finally, we present experimental evidence showing that L1 is involved in murine neocortical histogenesis and propose a hypothetical mechanism of L1‐linked hydrocephalus, with reference to corticogenesis.